Struggling with my relationship with my step kids: Any advice?

I fought actively next to my fiance to get his kids out of foster care.  I did everything he did legally to have them in my house. The worst part is the two teenagers could care less. They are continuously telling lies on us. They have continuously made life a living hell in the household. They are not grateful for anything that we have done for them.  It has been three years and everything has blown up. They got CPS involved with lies, and with CPS knowing they are lies, its just gotten worse here. They are ungrateful for everything that has been given to them, and I have taken the option of stepping back from parenting. They have taken my happiness in my own house away. They disrespect me as a person every day. They laugh and make fun of me for being hurt. I am second guessing myself everyday on what kind of person I am, I have always always been a good person until they have taken over. I need help!